The classification of the protozoa on this page is quite outdated and somewhat arbitrary
(and incomplete: I only showed the genera I have encountered so far).
It follows the systematic classification in the 'How to know protozoa' book by Jahn et al (1979).
For every genus, two contemporary taxonomical sources are cited: Integrated Taxonomy Information
System and NCBI Taxonomy Browser (where available).

Ciliates are the most complex group of protozoa. Their cell body is covered with
cilia.
The
cilia
sometimes differentiate into unique structures like cirri
or
membranelles.
Ciliates have two kinds of nuclei: macro- and micronuclei.

Mastigophora (the Flagellates) are protozoans propelled by one or more
flagella.
Some exhibit
pseudopodia.
They usually reproduce asexually by binary fission, but some species reproduce sexually by syngamy.

Class Euglenea

Often have a red stigma at the
anterior
end and green chloroplasts. One or two
flagella.
Cell contains
paramylum bodies.

Medium-size flagellates. They have two
flagella:
a circumferential one placed in a transverse groove -
girdle,
and a longitudinal one, placed in a posterior groove -
sulcus.
Many species have yellow-brown chloroplasts.

Order RadiolaridaRadiolaria are marine, pelagic organisms,
exhibiting a complex endoskeleton, formed with silica, often radially symmetrical and very beautiful.
The endoskeleton (central capsule) covers a nucleated part of the cell.